void main() {
  const count = 20;
  const count2 = 10;

  const safeTop = count + count2;
  final safeBottom = count + count2;
  print(safeTop);
  print(safeBottom);
  //const 是编译期常量，在编译时赋值
  //final 是运行期常量，在运行时赋值
}
